This section provides background information related to the present disclosure which is not necessarily prior art.
Electromagnetically driven reciprocating pumps are used to convey and meter fuels and reagents. They can be manufactured economically, and can, due to their pulsed mode of operation, be operated with adjustable conveyed quantities if the frequency of the pulse is changed.
Electromagnetically driven reciprocating pumps consist of an electromagnet and a fluid displacement unit into which the working fluid is sucked, from which it is ejected and subjected to pressure. The electromagnet and the displacement unit are in most cases inseparably connected together by common components, and if the structural form of a through-flow electromagnet is chosen, no rod seal is needed between the electromagnet and the displacement unit.
One disadvantage of the usual mode of operation of these displacement pumps is associated with current being fed through the magnetic coil until the movement of the magnetic armature has finished, or even for a longer period; this is necessary if a complete travel is to be achieved under all operating conditions without taking further measures.
The current feed described above results in a hard impact of the magnetic armature, with correspondingly high noise and low efficiency of the electromagnetic drive.
A hard impact also correspondingly results during a return of the magnetic armature to the rest position if the return springs move the magnetic armature back without braking when the electromagnet is switched off.
Various methods for overcoming the said disadvantages are known from the patent literature, but these are in some cases very expensive and in some cases unsatisfactory.                Document DE 199 82 757 B4 describes a method for driving a fuel metering pump in which both electrical and fluid state variables are measured, and the measured values are used to change the voltage at the electromagnet.        Document DE 10 2004 002 454 B4 describes a method for operating a metering pump in which a duty ratio for modulation of the supply voltage is changed during a drive interval.        Document DE 101 27 996 A1 describes a pump apparatus and a regulation apparatus in which the position of the magnetic armature is deduced from a measurement of the curve of the coil current, and the voltage is switched depending on the position, in order to brake the magnetic armature before it reaches the end stop.        Document DE 100 33 923 A1 describes a method for determining the velocity and position of electromagnetic actuation systems without using sensors. The position is determined here from the changes in voltage and current caused by the movement of the armature.        Document DE 100 20 896 A1 describes a method for determining the position of an armature/a valve. The current in, and potentially the voltage drop across, an exciter coil is here determined, from which the magnetic flux through the exciter coil is determined. The displacement position is then determined by means of a characteristic map which represents the relationship between the flux and the position.        
The known methods all exhibit at least the following disadvantages:                The changes in the ambient conditions of the controller and the reciprocating pump, in particular changes to the supply voltage and to the coil temperature, are inadequately detected and considered, and this impairs the quality of the control method.        The estimation method for the travel of the magnetic armature is not based on a mathematical model of the driving electromagnet, and this means that only a very rough approximation can be performed, in particular as a result of the non-linear behaviour of electromagnets.        Existing knowledge about the electromagnet used, which can be determined on a test bench with reasonable effort, is inadequately recognized and considered, if at all, whereby again the quality of the control method suffers.        
In the dissertation “Entwurf von magnetischen Mini- and Mikroaktoren mit stark nichtlinearem Magnetkreis” (Design of magnetic mini- and micro-actuators with highly non-linear magnetic circuits) by Dr. M. Kallenbach (TU Ilmenau), a method for estimating the position of a magnet on the basis of measured values of voltage and current and of calculated values for the linked magnetic flux is described; it also determines highly accurate values for the magnet position even for non-linear magnetic systems. An application of the method to the control of a reciprocating pump is not described.